The studies outlined in this proposal are based on a unique genetic approach to identify genes that are essential for the function of either the male or female gametes of Arabidopsis thaliana. In particular, the focus of this proposal will be on the critical molecular events that allow the male gamete-bearing structure, the pollen grain, to germinate, invade the ovary and successfully achieve fertilization of an ovule. These experiments take advantage of the quartet mutation, which causes the four products of pollen meiosis to remain fused, without adverse effects on individual pollen grains. T-DNA mutagenesis of quartet using a reporter gene that is expressed only in pollen enables detection of insertions into genes that are essential for either male or female gametes by a rapid and efficient visual screen. Lines carrying these types of insertions can be identified because they will fail to produce individuals that are homozygous for the insertion. This approach offers a unique opportunity to study the function of genes that will not be isolated by traditional genetic screens. In addition, the T-DNA allows direct analysis of mutant pollen phenotypes so that mutations can be isolated that disrupt each of the critical steps in pollen function, allowing a thorough mechanistic study.